It is conventional, for example, in tableting to add the mixture to be tableted ("aggregate"), in addition to other auxiliary and carrier substances, also so-called lubricants (also known as sliding or separating agents), as well as, if necessary, to spray the mixture therewith. These are generally intended to reduce the friction of the dies moving up and down in the matrix bore and also the sliding friction between the tablet gate and matrix wall; furthermore, they have to generate a separating or anti-adhesion action so that the pressed articles are detached perfectly from the molding tools.
Intermixing or spraying of the lubricants presents a series of well known disadvantages. Lipophilization (water-repelling action) occurring on the surfaces of the individual articles generally causes in tablet manufacture, apart from poorer pressing capacity, also an increase in the decomposition of the molded articles. The resultant low breaking strengths of the molded articles have to be improved again by the increased use of expensive binding agents. In the case of pressed articles of active substance, lipophilization of the surfaces and the increased use of binding agents may result in a reduction in bio-availability. Since the negative effects of the lubricants are extraordinarily dependent on the manufacturing conditions (size of mixture, type of granulating apparatus, type of mixer, etc.), when these substances are used, it is also necessary to allow for the negative effects on the bio-equivalence of individual production batches. Finally, in the case of a number of active substances intermixing of the lubricants (e.g. magnesium stearate) has a negative influence on active substance stability, added to which is the fact that in certain applications the lubricants are responsible for the poor flavor of the pressed articles.
Attempts have therefore already been made to abandon completely the admixture of lubricants and, instead, to coat with lubricants the mold or press compartment which is formed by the matrix bore and the active parts of the upper and lower die and in which the tablet or molded articles is pressed. Here, especially for the manufacture of so-called effervescent tablets in which it is important to ensure rapid decomposability and clear dissolving, a method has been developed in which after each pressing operation the pressing tool is coated by the extrusion of a so-called "lubricating granulate" (empty granulate) (see German Offenlegungsschrift No. 2,440,383). This method has, however, the disadvantage of a higher consumption of time owing to the necessity of preparing the lubricating granulate and to a considerable reduction in the capacity of the tableting machine. Also, this method is suitable exclusively for double-sided tablet presses.